Prescribing for patients with low eGFR: Where should you start questioning? Hospital pharmacist thought steps [4 perspectives to prevent oversight]

Don't you ever feel nervous
every time you receive a prescription?

“I feel like this patient had poor kidney function...”
“At what eGFR level should I start worrying?”

I used to worry when looking at prescriptions during my first or second year too.

Now, as a hospital pharmacist,
I face prescriptions for patients with reduced kidney function almost every day.
Now that I have gained experience, “It's fine if the eGFR is 60 or higher”
—I feel that this kind of mental autopilot is the most dangerous thing.

In this article,
as a pharmacist certified by the Japanese Society of Nephrology and Pharmacotherapy,
I will share the “way of reading kidney function”
that unfolds in my mind when I receive a prescription,
using the most direct language possible.

—And this article is also
the introductory article to my note magazine, “Stories of Kidneys and Drugs: Thought Steps for Hospital Pharmacists”.

📑 How to navigate the 15 Kidney Magazine articles

🚪 [You are here] Read first: The overall picture of the thought steps
→ This article

🔬 Read next: Questioning the “appearance” of kidney function evaluation

💊 The gut-kidney axis and constipation

💭 Stories of difficult decisions (Pregabalin, the choice not to dialyze)

Now, let's begin with the 4 perspectives👇

That was
back before I started studying kidneys in earnest.
The eGFR was 60 or higher.
In the “normal to mildly reduced” range.

I judged it that way,
and let the prescription pass as is without even making an inquiry.

That patient experienced side effects.
No one pointed it out, and
it never became a topic at the conference.

I realized that I had “done something terrible”
much later,
when I continued to study the kidneys.

What was I overlooking back then?
I broke into a cold sweat all by myself.

I didn't know the reason for that at the time.
Without knowing, I judged that "it's fine because the numbers are in the normal range."

I didn't truly understand
—that there was a patient on the other side of the prescription.

Now, when I pick up a prescription,
multiple thoughts run through my mind simultaneously.
It's a "critical eye" cultivated in the field,
not found in textbooks.

There arefourthings I always check.

I organize these four points using three "eyes."

Today, I would like to reveal that thought process
in order.

Step 1 | Question the "apparent values"—Look at the muscles

First, let's start with "don't trust the eGFR of people with low muscle mass too much."

As I continued my studies, there was one thing I understood first.

Creatinine is a metabolic byproduct of muscle.
In other words—
people with less muscle have lower creatinine levels.

And eGFR is
calculated based on creatinine levels.
As a result, the eGFR of patients with poor muscle mass
is calculated to be "higher" than the reality.

Kidney function looks normal, but it is actually declining.
This is"masking."

In convalescent rehabilitation wards,
there are many patients whose sarcopenia has progressed due to long-term bed rest.
For such patients,
the eGFR number"lies."

When I learned that,
I found one "solution."

The Round-up method (0.6 substitution method).

When the creatinine level is too low,
the method is to replace it with 0.6 for calculation.
I thought I had found something good.
I used this frequently.

However, I learned later.
The roundup method is a tool to 'prevent overestimation,' not a tool to 'evaluate accurately.'

'It's safe if you put in 0.6'
—you must not stop there.

So, how can we evaluate the renal function of patients suspected of having sarcopenia
more accurately?
That is where Cystatin C comes in.
I have written about the detailed mechanism and clinical usage in another article.

▶ Next article (scheduled for release on April 24th)
[Do not trust an 'eGFR of 90' in bedridden elderly patients. The real reason pharmacists want 'Cystatin C']

By the way, regarding sarcopenia,
Tanuzaishi-san's article was very easy to understand, so please use it as a reference.

So, what does it really mean to
'look at the muscles'?

It means looking at that person's activity level.

I first go to the patient.
It doesn't have to be a direct conversation, and it can be from a distance.

I look at the whole person with the eyes of,
'I wonder what their muscle mass is like.'

If the environment allows me to go to the ward,
I check the CC (calf circumference).
The registered dietitian or rehabilitation staff
might have already measured it.

If that is difficult,
I open the rehabilitation evaluation sheet.
I look at the 'mobility' item of the FIM.
Wheelchair use or total assistance
—that is a sign that muscle mass has decreased.

Look at the patient before the eGFR number.
When I feel that 'muscle mass is low,'
the option of measuring Cystatin C
begins to move.
I now believe that order is important.

Step 2 | Remove the 'makeup' of standardized eGFR—let's look at the units

Next, the story that the eGFR listed in the test values
is a 'number that cannot be used directly for dosage calculation.'

A petite grandmother in her 80s.
The creatinine level is 0.4.
The eGFR (mL/min/1.73m²) listed in the test values
is over 100.

'Any drug can be used at the normal dose'
……is that really true?

I believe whether or not you can stop here
is the turning point.

The eGFR (mL/min/1.73m²) listed in the test values is
a value corrected to a standard body type (body surface area of 1.73m²).
In other words, it is a number with makeup on, so to speak, saying 'if this person were a standard body type, their renal function would be about this much'.

A petite elderly woman in her 80s
cannot possibly have a standard body type.
Therefore, I remove that makeup.

I calculate the body surface area and
multiply it by the standardized eGFR.
Only then does
the patient's true renal function (individualized eGFR, mL/min) appear.

That figure, with the correction removed,
becomes the basis for determining the drug dosage.

An eGFR corrected for 1.73
can be used for 'screening' renal function.

ButI do not use it when considering dosage.
This is one of the ironclad rules I was taught first when studying the kidneys.

Even if a petite elderly woman's eGFR exceeds 100,
her individualized eGFR can be less than half that.
That difference is the difference between an overdose and an appropriate dosage.

If you don't question the numbers,
you will end up giving the patient the wrong amount of medication.

▶ Click here for a detailed explanatory article on renal function evaluation

Step 3 | Seeing through the trap behind 'addition'—Look at the cascade

By tracing the history of prescriptions one by one,
you can sometimes see the 'real reason' why the number of medications increased.

A patient with underlying dementia.
One day, they complained of heartburn, and famotidine was started.

After a while, the patient began to change.
They became unusually irritable and
started refusing care.
They began shouting loudly
at other patients.

All the ward staff thought,

We changed the environment.
We changed how we spoke to them.
But it didn't have much effect.

Yokukansan was started to suppress the agitation.
It seemed to calm them down a little,
so it was continued for over half a year.

Before we knew it, their legs were swollen.

'Given their age, it might be heart failure'
—a diuretic was added.

They complained of frequent urination,
so a medication for frequent urination was also added.
The prescription had expanded without us realizing it.

The starting point of this chain was the very first move.

Starting famotidine.

The creatinine level was 0.3.
The standardized eGFR was over 100.
That is why a standard dose was chosen.

However, the patient's ADL at that time was wheelchair-bound,
or bedridden.
The body weight was in the low 40 kg range.

The 'masking' I mentioned in Step 1
is happening here too.
A small body with little muscle mass.
Creatinine levels appear low.
eGFR appears high.
But the true renal function
must have been much lower than those numbers.

Famotidine is a renally excreted drug.
If evaluated using an individualized eGFR,
I believe it was a state that required dose reduction.

Could the psychiatric symptoms caused by overdose
have triggered the agitation?
Perhaps long-term administration of Yokukansan
caused edema.
Diuretics increased the frequency of bathroom visits.
If the famotidine dose had been adjusted at the beginning,
this chain might have been prevented.

This is what a prescribing cascade is.
'Side effects of medication' look like 'new symptoms',
and 'new medications' are added.

No one is to blame.
Everyone is doing their best to treat the patient in front of them.
But without realizing it, medications increase,
and they begin to erode the patient's health.

That is why, when I pick up a prescription,
instead of just adjusting the medication dosage,
I trace the history of the prescription.

I ask, 'Why was this medication started?'
Because behind the addition, there is sometimes a hidden opportunity for subtraction.

Step 4 | Incorporating into 'daily life'—Look at the reality at the bedside

Finally, this is about extending your imagination outside the hospital—to life after discharge.

One patient
was readmitted two months after discharge.
It was acute kidney injury.

Tracing the cause,
they had been using over-the-counter painkillers for lower back pain.
They had been weeding in the summer and became dehydrated.
That combination put pressure on their kidneys.

At the time of discharge, I told them, 'Please make sure to take your medication.'
The patient replied, 'I understand.'

That patient kept that promise properly.
They continued to take the prescribed medication.
To manage the pain on their own,
they bought painkillers at the pharmacy.
Even with the weeding,
I believe they were trying to do things for themselves.

Everyone did their best.
Even so, the result was acute kidney injury.

When I received the news of the readmission,
I truly regretted it.
Could I have done something more?
What kind of guidance could have prevented the readmission?
Should I have thought more about
their life after discharge?

But to be honest, in the midst of busy daily tasks,
I don't even imagine
the patient's 'weeding the garden in summer' after discharge.

Even now, I don't know the correct answer.
However, ever since that readmission,
there is something I make sure to tell
every patient I am involved with.

Just that.
It's not perfect guidance.
It doesn't prevent everything.
But I don't just adjust the numbers and finish.
I imagine together with them, just a little,
what kind of season they will spend after discharge.
That is what I can do now,
which is 'looking at their life'.

Tomorrow, when you pick up a prescription,
if you are in an environment where you can check, even for just one person,
please go and look at the FIM and CC of a patient
you think 'seems to have low muscle mass'.
Just by doing that, the view you see should change a little.

Conclusion | To you who are fighting in the field

When I line up the 4 steps,
I feel like they are all saying the same thing in the end.

Even if eGFR is normal, look at that person's muscles.
Even with standardized values,
correct them with that person's physique.
When you see the addition of prescriptions, question their history.
Even if you adjust the amount of medicine, imagine that person after discharge.

None of these are in textbooks.
But back then, when I was doing things by the book,
I wasn't able to fully protect my patients.
Without anyone pointing that out to me,
I realized it alone much later.
I still haven't forgotten
that day when I broke out in a cold sweat.

In practicing the 4 steps,
there is one more important thing.

'Questioning the numbers' is not enough.
When you question them, do you have the tools to provide an alternative answer—that is the point.

Even if you notice in Step 1 that 'this eGFR cannot be trusted',
then how do you evaluate the true renal function?
One of the answers to that is Cystatin C.

A 'perspective to question' and 'tools to evaluate correctly'.
I believe that only when these two are in place can you protect the patient on the other side of the prescription.

Tomorrow, when you pick up a prescription.
Please try to imagine, just a little bit,
what is beyond that paper.

That's all for this time.
Thank you for reading.

▼Things I want you to read along with the lingering effect of this article

▶ For those who want to know 'concrete ways to move' after using the thought steps

▶ For those who want to protect CKD patients by collaborating with rehabilitation professionals

▶ For those who want to read about how to create your own place as a young pharmacist